Compositions and process for the electrodeposition of metals

ABSTRACT

An electrically conductive medium for the electrodeposition of metals comprises an aqueous solution of (a) a metal ion, (b) a carboxy alkylene amino di(methylene phosphonic acid) and optionally, (c) 1-hydroxy alkylidene-1,1-diphosphonic acid.

United States Patent 1191 Kowalski 51* Oct. 21, 1975 1 COMPOSITIONS ANDPROCESS FOR THE [56] References Cited ELECTRODEPOSITION OF METALS UNITEDSTATES PATENTS [75] Inventor: Xavier Kowalski, St. Louis, Mo. 2,673,2143/1954 Bersworth et al 260/5025 2,961,311 11/1960 Bersworth et a1 1.260/5015 X [73] Asslgnee' clmpalw Lows 3,293,176 12/1966 White 260/5025X [*1 Notice: The portion of the term of this Z1323 fichieferm 32 aynesg g?? 5 3 3,617,343 11/1971 Kandler 117/47 R as e almfi 3,706,63512/1972 Kowalski 204/46 22 i J 25 1973 OTHER PUBLICATIONS [21] Appl.No.: 373,051 H. Koretzky, IBM Tech. Disclosure Bulletin, Vol. 9, [44]Published under the Trial Voluntary Protest 1634 Apnl 1967 Program onJanuary 28, 1975 as document no. B 373,051. Primary ExaminerG. L. KaplanAttorney, Agent, or FirmThomas B. Leslie [52] US. Cl 204/46 G; 204/43 R;204/44; 204/46 R; 204/48; 204/49; 204/50 R; 204/51; 204/52 R; 204/55 R;260/5025 [57] ABSTRACT 2 6 [51] CL C251) 3/04 C251) g ga i Anelectrically conductive medium for the electrode. [581 Field Of Search204/45-55, Position of metals comprises an aqueous wlutlo of (a) a metalion, (b) a carboxy alkylene amino di(- methylene phosphonic acid) andoptionally, (c) 1- hydroxy alkylidene-1,l-diph0sphonic acid.

10 Claims, N0 Drawings COMPOSITIONS AND PROCESS FOR THEELECTRODEPOSITION OF METALS BACKGROUND OF THE INVENTION 1. Field of theInvention The present invention relates to the electrodeposition orelectroplating of metals. More particularly, the present inventionrelates to the composition of the electroplating bath from which themetal is deposited.

2. Description of the Prior Art The electrodeposition of metals fromaqueous solutions of metal ions is an old art. The typicalelectroplating system consists of an electroplating bath and two or moreelectrodes. The cathode of the electrode system is the object to beplated. The anode may be carbon or a solid piece of the metal to beplated upon the cathode. A solid metal anode is consumed in theelectroplating process and provides a constant source of metal ions tothe plating bath.

Metal ions are maintained in solution in the electroplating bath byforming salts or metal complexes. Some of the most popular platingcompositions utilize inorganic metal cyanides, and cadmium, brass,copper, silver and zinc can all be plated from cyanide baths.

Electroplatingbaths comprising aqueous alkaline solution of metalcyanides have several disadvantages. Such baths often tend to producerelatively dull and uneven coatings of the plated metal. The use ofmetal cyanide solutions can also be hazardous since if the pH of theelectroplating medium should drop to neutral or below there is a dangerof poisonous hydrogen cyanide gas being produced. Also, the use of metalcyanides presents a disposal problem due to their toxicity, and removingcyanides from waste baths prior to disposal is an expensive undertaking.

The prior art has suggested certain techniques for improving theperformance of cyanide plating baths or for even eliminating cyanidefrom the bath. US. Pat. No. 2,195,409 claims to improve the performanceof metal cyanide baths by the addition of a nuclear alkyl derivative ofan aromatic sulfonic acid of the benzene series. The presence of thismaterial is reported to eliminate pitting, uneven thicknesses and theformation of pinholes in the metal plate, and also improve brightnessand uniformity of deposits.

More recently it has been suggested to use certain metal complexingagents in cyanide free plating baths. U.S. Pat. No. 3,457,293, forexample, suggests the use of certain diphosphonates or monoamino loweralkylene phosphonates in the electroplating of divalent metal ions. US.Pat. No. 3,706,634 and 3,706,635 suggest combinations of ethylenediamine tetra( methylene phosphonic acid), l-hydroxy ethylidene-l ldiphosphonic acid, and amino tri(methylene phos phonic acid) asparticularly useful complexing compositions. US. Pat. No. 3,617,343 issimilarly directed toward a nickel plating system employing certainphosphonic acid compounds. The present invention supplements andimproves upon these methods of the prior art by providing certainorganophosphorus compounds not taught in the prior art which are usefulin electroplating applications.

SUMMARY In accordance with the present invention there is employed asthe electroplating bath an aqueous solution comprising (a) a divalent orpolyvalent metal ion; (b)

a carboxy alkylene amino di(methylene phosphonic acid) having thestructure CH (OM) MOOC (CH N pound having the structure I M O P C PO Mwherein M is as above defined and R is an alkyl radical having from 1 toII and preferably from l to 5 carbon atoms. Such electroplating bathcompositions are particularly useful in plating divalent metal ions at apH of about 6.0 to 10.0.

DESCRIPTION OF PREFERRED EMBODIMENTS In the practice of the presentinvention the metal to be plated in conjunction with the carboxyalkylene amino di(methylene phosphonic acid) compound (hereinafterreferred to as carboxy amino phosphonate or CAP) is preferably adivalent transitional metal such as copper. iron, nickel, zinc, cadmiumor alloys 5 such as brass. Monoand trivalent metals. however.

such as silver, chromium, and gold, may also be electorplated inconjunction with CAP and are included within the scope of the presentinvention.

The electroplating bath composition of the present invention is anaqueous solution comprising the metal to be plated, the carboxy aminophosphonate, pH adjusters and optionally one or more additives includingbrighteners, buffering agents, levelers, and the hydroxy alkylidenediphosphonic acid compound (HAD?) 5 which are intended to improve theperformance or life of the bath or the quality of the metal deposit, orto impart other beneficial effect. It is common in the electro' platingart to utilize many and varied additives which are selected according tothe particular system being used and on the basis of the skill of theelectroplater. The use of such additives in the electroplating bathcompositions of the present invention in order to adapt thesecompositions to individual circumstances are included within the scopeof the present invention.

The bath is prepared according to conventional techniques by simplydissolving the desired ingredients into a quantity of water. The wateris preferably low in mineral content and may be deionized. The metal tobe plated is often added in the form of a water soluble salt such as ametal sulfate, chloride, phosphate, citrate, carbonate or acetate.Carbonate and acetate salts are often preferred because the anions ofthese salts may be thermally decomposed and thereby removed from thebath when the metal ion is released.

The carboxy amino phosphonate may be added directly to the bath ineither the acid or a salt form as defined above. The acid form isgenerally preferred simply because it does not introduce extraneousmetal or ammonium ions into the bath, but the introduction of suchanions is usually not detrimental to the electroplating system. Whilethe alkylene radical of the CAP compound may have from 3 to about 1 1carbon atoms as defined above, the preferred compounds are those havingalkylene radicals of from about 3 to 6 carbon atoms. N-(S-carboxypentyl)amino di(methylene phosphonic acid) is one particularly preferred CAPcompound. CAP compounds useful in the practice of this invention may beprepared by the method of copending patent application Ser. No. 361,383,filed May 17, 1973, which is commonly assigned with the instantapplication and is incorporated herein by reference.

The optimum concentration of metal salt and CAP in the electroplatingbath will be largely determined by the identity of the metal and metalsalt, and by the characteristics of the individual electroplatingsystem. As a rule, the concentrations are limited primarily by thesolubilities of the compounds. Generally speaking, there is usuallyemployed sufficient metal salt and CAP to provide from about 1 percentto about 5 percent by weight of metal in solution and to provide a moleratio of CAP to metal of from about 1:1 to about 5:1. The optimum ratiowill again depend to some extent on the metal being plated and theconditions and composition of the electroplating bath but as a generalrule at least a slight molar excess of CAP is desirable and it isgenerally preferred that the mole ratio of CAP to metal ion be withinthe range of from about 1.2:1 to 2: 1. In most instances, theconcentration of complex formed between the metal ion and the CAP shouldnot exceed its solubility at the temperature and pH employed in theelectroplating operation.

The electroplating bath is generally operated within a pH range of fromabout 6 to 12. The optimum pH will depend to a great extent upon theidentity of the metal being plated, the presence of extraneous anionswithin the system and the composition and physical nature of the cathodebeing plated. Since pH is easily adjusted by the addition of alkalinematerials such as alkali metal hydroxides, or acid materials such asmineral acids, it is a relatively simple matter to adjust the pH ineither direction until optimum plating characteristics are achieved. Asa general rule it is often found that lower pH values, that is withinthe range of from about 6 to 8, give better results in the practice ofthis invention than higher pH levels although exceptions to this rulemay be found.

The use of the HADP compound (c) as defined above, is found to enhancethe performance of the electroplating bath, particularly with respect tothe plating copper. HADP compounds useful in the practice of the presentinvention may be prepared according to the method of U.S. Pat. No.3,551,480. A particularly preferred HADP compound is l-hydroxyethylidene-1,l-diphosphonic acid (HEDP). A combination of CAP and HADPis particularly effective to produce bright, uniform, and tightlyadhering deposits of copper on brass and steel by electroplating at a pHof about 8.0. The concentration of HADP used in the composition of thisinvention is sufficient to provide a mole ratio of HADP to metal of fromabout 0.5:1 to about 5:], although from about 1:1 to about 2:1 ispreferred.

While the aforegoing description is directed primarily to thecomposition of the electroplating bath, the

present invention further provides a process for the electrodepositionofa divalent or trivalent metal which comprises the steps ofelectrolyzing an aqueous solution of a metal complex consisting of anyof the metal ions hereinbefore described, a CAP compound, and any of theoptional additives hereinbefore described. By the process of thisinvention, metals such as copper, iron, nickel, zinc and cadmium may beelectrically deposited upon a cathode such as steel, aluminum, brass,zinc and the like.

During the electrodeposition process, the electroplating bath ismaintained at a temperature within the range of the freezing point toboiling point of the bath, generally within a range of from about 30C.to about C. For reasons of current efficiencies it has been foundpreferable to maintain the temperature of the electroplating bath withinthe range from about 50C. to about 80C.

The amount of current employed in the electrodeposition may vary widely,depending upon the particular metal being plated, the temperature of thebath and whether or not the bath is agitated during the electroplatingprocess. In general, the amount of current employed will be sufficientto provide a current density of from about 1 to 300 amperes per squarefoot of electrode surface. Ordinarily when the electroplating bath isquiescent or unagitated, the current density will be in the range offrom about 5 to amperes per square foot, while when the electroplatingbath is agitated current densities up to about 300 amperes per squarefoot may be utilized. The optimum or preferred current density for anyparticular electroplating situation will depend upon the individualcharacteristics of the operation and is readily determined by employingconventional electroplating techniques.

The time required to electroplate or to electrically deposit the metalwill vary with the kind of metal, the current density, and bathcomposition and concentration, as well as upon the thickness of theplate or deposit desired. Generally, the greater the current density,the shorter will be the time required to produce a metal deposit orplate of a given thickness.

In accordance with a preferred embodiment of the present invention,copper is electrically deposited upon a wide variety of base metals orsubstrates such as zinc, iron, brass, steel, aluminum and the like. Thispreferred process comprises passing an electric current, at a density inthe range of from about 5 to about 150 amperes per square foot ofcathode surface, through an aqueous solution containing divalent copperions and CAP or CAP HADP and having a pH in the range of from about 6.0to about 10.0 and preferably 6.0 to 8.0. The concentration of copper inthe electroplating bath composition is preferably from about 1% to about5 percent by weight, based on the weight of the solution. Thetemperature of the solution is preferably maintained within the range offrom about 50C. to about 70C. during the electroplating operation.

As stated above, the electroplating solutions of the present inventioncan contain known brighteners, buffers, and leveling agents and otheradditives commonly used in electroplating operations. Boric acid and itssalts are compatible buffers for many formulas of the invention, andselenites and arsenites are useful brighteners for copper plating bathswhile aldehydes and ketones are useful for zinc plating. Other additiveswhich may be employed in the electroplating solutions of the presentinvention include those disclosed in the 39th Annual Edition of MetalFinishing Guidebook Directory, 1973, published by Metals and PlasticsPublications, Inc., 99 Kinderkamack Road, Westwook, NJ.

tent agitation. The results of these tests are set forth in Table I andparticular attention is directed to the column designated BrightnessRating which provides the basic criteria for an evaluation of theelectroplating ef- Certain preferred embodiments of the present inven- 5fects on an overall basis.

TABLE I Test Additive/ Brightness No. pH Additive Cu Ratio CathodeRating Remarks on Brightness l 6.0 CAP 2:l Brass Good Dark heavy copperdeposit. 2 8.0 CAP 2:l Brass Poor Dark burn. 3 10.0 CAP 221 Brass PoorDark burn. 4 6.0 CAP 81. 2:1 Brass Fair-Good Dark heavy copper deposit.

HEDP lzl 5 8.0 CAP & 2:l (a) Brass Very Good Very bright, good cover.

HEDP 1:] (b) Steel Very Good Very bright, good cover and copperadhesion. 6 10.0 CAP & 2:] Steel Fair Dark burn.

HEDP lzl 7 6.0 HEDP 2:] Brass Fair Foggy, smudged. S 8.0 HEDP 2:l BrassPoor Smudged, Streaky, spotted. 9 10.0 HEDP 2:l (a) Brass Good Bright,smudged.

(b) Steel Good Bright, smudged. good copper adhesion.

CAP N-(S-carboxypentyl) amino dimethylene phosphoric acid HEDP l-hydroxyethylidene-l.l-diphosphonic acid tion concerning the electrodepositionof copper are illustrated by the following Example which is not limitingof the invention. All parts and percentages are by weight unlessotherwise specified.

EXAMPLE Eleven tests were conducted to illustrate the performance of CAPalone and a combination of CAP and HEDP as compared to HEDP alone in theelectrodeposition of copper from an electroplating solution con tainingthese additives.

The plating solutions identified as Test Nos. 1-9 in Table I wereindividually prepared in deionized water by dissolving measured amountsof CAP and/or HEDP and copper sulfate to provide 2 percent copper andthe molar ratio of CAP/HEDP/Cu indicated in Table I. The pH of eachsolution was adjusted to the desired value of 6.0, 8.0, or 10.0 by theaddition of potassium hydroxide. When necessary to dissolve the coppersulfate, the solution was heated up to 80C. and stirred vigorously foran additional minutes. The solutions were cooled, if necessary, to theplating temperature of 70C. and transferred to a Hull Cell". Theparticular additive utilized, the additive of copper mole ratio and thepercent copper in solution are all shown in Table I.

The Hull Cell is constructed substantially as the electrolysis celldescribed in US. Pat. No. 2,149,344. This type of Hull Cell is standardequipment for the evaluation of electroplating solutions by thesubjective determination of brightness rating" as based on the width ofthe brightness range, uniformity of brightness, and the presence orabsence of smudges, stains and discoloration. In addition, theeffectiveness of the bath is also evaluated on the basis of adhesion ofplated metal to the cathode. The particular cathodes utilized in thistest were brass or steel as indicated in Table l and were each 5 X 3 /4inches in size. The anode utilized in these tests was made of copper andwas 2% X 2% inches in size. The Hull Cell utilized in this test had acapacity of 1,000 milliliters.

Each test was conducted for a period of two minutes at a constantcurrent of two amperes and with intermit- Tests Nos. 4-6 in Table 1illustrate the advantage gained by utilizing HEDP in combination withCAP. A particular advantage, is noted at pH of 8.0 (Test No. 5) where aBrightness Rating of very good" was registered for plating on both brassand steel cathodes. It was also observed that copper adhesion on steelwas very good under the conditions of this test. Test No. 5 accordinglyrepresents a particularly preferred embodiment of the present invention.

Tests Nos. 7-9 are controls illustrating the results obtained with HEDPalone under similar electroplating conditions. It is observed that HEDPperforms best at the higher pH of 10.0, but the quality of the plate isstill inferior to that obtained with the combination of CAP and HEDP.

With further reference to the date in Table I, it is observed that thecombination of CAP and HEDP gives at least fair results over the entirepH range, and that at a pH of 8.0, the combination gives significantlybetter results than can be obtained with either component aloneregardless of pH.

Although the invention has been illustrated by reference to theelectrodeposition of copper utilizing the method and compositions ofthis invention, the present invention is not limited thereto but is alsouseful in electrodepositiong other metals electrodepositing othercathode materials as hereinabove described. Ac-

cordingly, the present invention is not to be limited except as definedin the claims appended hereto.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A process for the electrodeposition of divalent and polyvalent metalions which comprises the steps of electrolyzing an aqueous solutioncomprising a. a divalent or polyvalent metal ion,

b. a carboxy amino phosphonic acid compound of the structure CH PO MMOOC (CH N CH PO M I and wherein M is hydrogen, alkali metal, ammonium,alkyl ammonium, or amine, n is an integer of from 3 to about 11 and R isa C, alkyl radical; the concentration of (a) in said aqueous solutionbeing from about 1 percent to 5 percent; the molar ratio of (a):(b)being from about 1:1 to 1:5; and the molar ratio (a):(c) being fromabout 2:1 to 1:5; the pH of said aqueous solution being from about 6.0to 10.0, and the temperature of said aqueous solution being from about30 to 90C.

2. A process of claim 1, wherein (b) is CH POM MOOC (CH N 6. Anelectroplating bath composition comprising an aqueous solution of a. adivalent or polyvalent metal ion,

b. a carboxy amino phosphonic acid compound of the structure CH POM 5MOOC (CH n CH PO M and c. a l-hydroxy alkylidene-l,l-diphosphonic acidcompound of the structure C PO MOP- 32 cu PO M MOOC (CH 8. A compositionof claim 7 wherein R is CH 9. A composition of claim 8 wherein saidmetal ion (a) is copper,

10. A composition of claim 6 wherein said metal ion (a) is selected fromthe group consisting of copper, iron, nickel, zinc, and cadmium, silver,chromium and gold.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 0 PATENT NO.3,914,162

DATED 3 October 21 1975 INVENTOMS) I Xavier Kowalski It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown beiow:

Col. 5, line 4, "Westwook, N.J. should read 1 Westwood, N.J.

Col. 6, line 27, "brightness" should read brightness Col. 6, line 45,"date" should read data Col. 6, line 55, "electrodepositiong othermetals electrodepositing other cathode materials as hereinabovedescribed." should read electrodepositing other metals upon othercathode materials as hereinabove described Col. 8, line 25, Claim 7, "Acomposition of claim 1" should read a A composition of claim 6 Engnedand Sealed this sixth [SEAL] D y of Aprll1976 Arrest:

RUTH 3 2:3" c. MARSHALL DANN a Commissioner oflarents and Trademark

1. A PROCESS FOR THE ELETRODEPOSITION OF DIVALENT AND POLYVALENT METALIONS WHICH COMPRISES THE STEPS OF ELEDTROLYZING AN AQUEOUS SOLUTIONCOMPRISING A. A DIVALENT OR POLYVALENT METAL ION, B. A CARBOXY AMINOPHOSPHONIC ACID COMPOUND OF THE STRUCTURE
 2. A process of claim 1,wherein (b) is
 3. A process of claim 1 wherein R is -CH3.
 4. A processof claim 3 wherein said metal ion (a) is copper and the pH of saidaqueous solution is about 8.0.
 5. A process of claim 1, wherein saidmetal ion (a) is selected from the group consisting of copper, iron,nickel, zinc, and cadmium, brass, silver, chromium and gold.
 6. Anelectroplating bath composition comprising an aqueous solution of a. adivalent or polyvalent metal ion, b. a carboxy amino phosphonic acidcompound of the structure
 7. A composition of claim 1 wherein (b) is 8.A composition of claim 7 wherein R is CH3.
 9. A composition of claim 8wherein said metal ion (a) is copper.
 10. A composition of claim 6wherein said metal ion (a) is selected from the group consisting ofcopper, iron, nickel, zinc, and cadmium, brass, silver, chromium andgold.